1. Field of the Invention
The present invention relates to a process for making selected carboxylic acid-containing monoether and polyether polyol addition products. The present invention also relates to these addition products as compositions-of-matter. The present invention further relates to polyurethane prepolymers and aqueous polyurethane dispersions made from these addition products, along with the processes for making these latter products. Still further, the present invention relates to the processes for using these aqueous polyurethane dispersions as coatings, adhesives, and other useful products.
2. Description of the Prior Art
Reactions of carboxylic acids with polyols are well known. The best known reaction between these compounds is the formation of polyester polyols wherein the acid groups react with the OH groups in the polyol.
Other reactions have also been taught. U.S. Pat. No. 4,250,077 (von Bonin et al.) teaches mixing olefinically unsaturated carboxylic acids with many types of polyols and then polymerizing the mixture with a free-radical former to produce a graft polymer. The preferred carboxylic acid (and the only acid used in the working examples) is acrylic acid, which homopolymerizes with itself. It should be noted that his reference does not teach the exact mechanism by which this "polymerization" reaction is carried out.
U.S. Pat. No. 4,365,024 (Frentzel) teaches making surfactants suitable for incorporation in polyurethane foams by reacting under free radical polymerization conditions a polyoxyalkylene adduct and an esterified unsaturated dibasic acid containing 4 or 5 carbon atoms. The mechanism of this reaction is referred to as grafting, i.e. the reaction product is composed of the polyoxyalkylene adduct backbone to which are attached at intervals "grafts" of the unsaturated diester. See column 4, lines 46-51 of this patent. The patent further states that "In light of the known inability of unsaturated diesters of the invention to homopolymerize, it is believed that the mechanism of the reaction may involve the addition of single diester units to the polyoxyalkylene backbone". The patent specifically teaches that these surfactants may be used in phenolic resin foams, polyisocyanurate foams and polyurethane foams.
Until the present invention, no one has proposed the free-radical addition of single carboxylic acid units at intervals onto the backbone of an oxyalkylene adduct (i.e. not at the --OH terminals as in polyester formation). It was quite surprising to find that selected carboxylic acids will react with polyhydroxy-containing monoether or polyether compounds in the presence of selected free radical initiators to attach single acid units at intervals onto the backbone of these ether-containing compounds. However, it should be noted that not all carboxylic acids or free radical initiators may be used for this reaction; only those defined below. Furthermore, it was found that these selected carboxylic acid-containing mono- and polyether products have a particularly advantageous suitability for making aqueous polyurethane dispersions. The single acid units on the backbone provide adequate sites for reaction with a neutralization agent to make a stable aqueous dispersion from the product, yet are short enough so that the viscosity of the product is not undesirably high.